Protective device for electric circuits



De@ 3l, 1929. H, M BAsCoM 1,741,356

PROTECTIVE' DEVICE FOR ELECTRIC CIRCUITS med Feb. 24. 1928 n 71 n' 7b suasfamm v ceurmooi- Eyurjomelz 4..

lNvENToR JI. msconz A ORNEY Patented Dec. 31, 1929 UNITED STATES PATENT OFFICE HENRY M. BASCOM, OF BROOKLYN, NEW YORK, ASSIGNOR TO AMERICAN TELEPHONE AND TELEGRAPH COMPANY, A. CORPORATION OF NEW YORK PROTECTIV DEVICE FOR ELECTRIC CIRCUITS Application led February 24, 1928. Serial No. 256,677,

This invention relates to protective devices for electric circuits, and, more particularly, telephone circuits.

A particular adaptation of the improved arrangement consists in its use as a protective device for telephone circuits in place of the heat coils and carbon block protectors ordinarily used for this purpose. The heat coils and protective block protectors require considerable time and effort in. their replacement. The protective block protectors also require considerable maintenance effort to bc expended in cleaning the dust and dirt which may accumulate thereon. Considerable maintenance effort is also expended in burnishing the contact surfaces between the heat coils and their mountings. It is an object of this invention to overcome these undesirable char-I acteristics by providing a protective device which may be positioned and replaced with minimum effort, and which will remain free from dust and dirt and require little or no effort to maintain it in operative' condition.

These and further objects of the invention will be more fully understood by reference to the accompanying drawing which illustrates a preferred embodiment thereof.

Referring to the drawing, 5 represents a tube which may be of a gas or vacuum type.

The tube 5 encloses filaments 6 and 7,. and an electrode or plate 8 thereby comprising an electric valve. The filaments are connected to a pair of conductors of the electric circuit to be protected, forV instance, a telephone circuit, which extends from a subscribers station to a central office. The conductors are designated by the numerals 9 and 10. The conductor 9, which may be the tip side of the line, extends from the substation to one terminal of the filament 6, and the other terminal of the filament is connected to the line which extends to the central oliice equipment. The conductor 10, which may form the ring side of the line, is connected to the filament 7 in a manner similar to that vdescribed in connection with the tip conductor 9.

The designof the filaments 6 and 7 is such that they will melt or rapidly deteriorate and thereby open the circuit when it carries a current in excess of predetermined limits. The plate 8, which is connected to ground, is so positioned adjacent the filaments that a difference in potential between either filament and ground in excess of predetermined limits will establish an electron discharge or arc discharge between the lament and plate, there- 4by grounding the conductor.

The resistance of each filament may correspond to the resistance of the usual heat coil which is associated with a subscribers line at a central office, and which will break down and open a circuit when subjected to abnor mal voltages and currents which mayfbe introduced in the subscribers line external to the central oiice.

What is claimed is: n Y

1. In a protector for electric circuits, the combination of a pair of line conductors, an electric valve associated therewith, said valve consisting of an evacuated vessel containing two independent filaments and a plate intermediate thereto, e'ach filament being serially associated with one conductor of the pair, and said plate being connected to ground.

2. In a protector for electric circuits, the combination of a pair of line conductors, an electric valve associated therewith, said valve consisting of an evacuated vessel containing a pair of filaments and a plate intermediate thereto, each filament being serially associated with one conductor of the pair, and

said plate being connected to ground, said 

